Transplant Basics

The mechanics of stem cell transplants are not often understood by the general population. To help gain a better understanding of the process, here is an overview of what happens before the transplant can happen.

Stem Cells

Stem cells are the core components of blood. They create the cells that make up all the other types of blood cells. What makes stem cells so important to a transplant is the fact that they can continuously reproduce themselves. People with certain cancers, genetic disorders or blood disorders whose blood and immune systems are not functioning properly benefit from the stem cells affect on their blood production.

Before stem cells are transplanted, scientists must first differentiate them. This means that the cells are influenced through the use of a signal to become a particular type of cell. Currently, this is the biggest hurdle for scientists. Experts aren�t exactly sure what signals cause the cells to change and therefore usually use chemicals to influence the manipulation of the cells.

Once this is done, the stem cells can then be transplanted, often by injection, into the patient. Exactly where and how the stem cells will be transplanted is determined by what part of the body it is hoped they will affect.

For example, children who have leukemia, a type of cancer that causes the body to produce too many white blood cells (WBC), will need chemotherapy to kill off the cancerous WBC. Since WBC are vital to a healthy immune system, the WBC that are killed through chemotherapy will need to be replaced. By manipulating cord blood stem cells to become WBC, healthy blood cells can be transplanted into the child�s blood stream thereby aiding in a full recovery from the cancer.

Finding a Match

Cord blood stem cell transplants are not necessarily for everyone. Because there are fewer stem cells found in cord blood than in bone marrow, it is typically thought that cord blood transplants are best suited to children and small adults (approximately 110 lbs). When a doctor is trying to find a suitable cord blood match, it is necessary for them to match the number of cord blood stem cells to the weight of the patient. However, it is possible for cord blood stem cells to be matched to many adults, as well.

Another consideration for doctors when trying to determine the best cord blood match for a patient is the number of identical Human Leukocyte Antigens (HLA) between the patient and the blood. HLA is a type of protein that is found on the outer surface of a cell. It consists of six groups of different antigens. Of these six groups, three are considered the most important in matching for a stem cell transplant. These are HLA-A, HLA-B, and HLA-DR. Each group is made up of two antigens, one from each parent. Therefore, doctors need to match a patient on six antigens.

A perfect match is referred to as a 6/6 HLA match, although doctors may do a bone marrow transplant if a patient is a 5/6 HLA match. However, with cord blood stem cells, a transplant can be done even if the recipient is a 4/6 HLA match. This is because the stem cells found in umbilical cord blood are not as mature as those stem cells found in bone marrow. Due to their immaturity, cord blood stem cells are less likely to attack a patient�s immune system, making a 4/6 HLA match more acceptable for a transplant.

Additionally, people who receive a cord blood stem cell transplant are less likely to experience graft versus host disease (GVHD). GVHD is when the immune system attacks the body after a transplant. This is a potentially fatal condition that can affect the skin and internal organs.


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